Which is better: fix or sell clunker?

GRAND RAPIDS, Mich. (WOOD) - When is enough enough when repairing your car?

Not everyone wants or can afford a new car. But if used cars are less available, the price of those used cars may go up.

And, car makers have cut their inventories. There are fewer trade-ins, which makes your used car more valuable -- and provides incentive for you to keep it in top shape.

Mechanics are used to seeing business go up when the economy goes down.

"For us it's been nice and even. We've had some growth over the last few years," said Todd Vruggink of Community Auto Repair. "We look at it as a full perspective. We ask, what are the goals for the car, how do they want to get to that goal, is it stretching out, minimal or are you really trying to get this car going for as long as possible."

Used car experts say the key is avoiding costly repairs in the first place.

"If you stay ahead of your car, it literally can run forever," said Jack Nerard of Kelley Blue Book. "Probably the least read book is the owner's manual of any car. Almost no one cracks that one open and there are so many good pieces of advice in a book like that."

To avoid costly repairs as your car ages:

change oil frequently. Consider synthetic oil. At least one brand, Valvoline guarantees a healthy engine for 300,000 miles.
change your coolant.
Keep your tires inflated and your wheels aligned.
Keep your car washed and waxed to avoid corrosion.

If you have to replace an expensive part, consider rebuilt parts, but make sure you get an ample warranty. You can also replace upholstery and ripped carpet for much less money than you'd shell out buying something brand new

Nerard said maintaining a car "and then repairing is less expensive than buying a new vehicle."

And Vruggink said he has customers "with over 350,000" miles on their cars.

Consumer Reports puts out a reliability guide every year, and also a "cost of ownership" guide that ranks cars by how expensive they are to maintain and repair.